There has long been a need to employ catalysts in reactions such as simultaneous combustion leading to oxidation of carbon monoxide and unburned hydrocarbons, and the reduction of nitrogen oxides (NOx) which are emitted from automotive engines and the like. The role of catalysts, particularly three-way catalysts, in automotive emission control has been widely studied in the art. For example, Taylor, "Automobile Catalytic Converter", Catalysis, Science and Technology, pp. 119-67 (Anderson et al. eds. 1984), describes emission control technology, composition of three-way catalysts and catalytic supports.
Conventional systems for converting automotive exhaust gases employ pre-fabricated supported catalysts, typically a solid stratum of catalyst material, such as honeycombed ceramic structures, which are placed in the exhaust section of the automobile. As the emissions pass through the solid, the catalytic metal present on the strata aids in conversion of CO, NOx and unburned hydrocarbons to CO.sub.2, N.sub.2 and H.sub.2 O. However, the solid strata-type catalytic converter eventually becomes spent, and requires removal and replacement in the exhaust portion of the engine. Moreover, structures such as a honeycomb support are complex and relatively expensive to manufacture. State of the art systems capable of carrying out three-way catalysis include those having supported noble metals such as rhodium and platinum, with rhodium being a preferred catalyst for the reaction: EQU NO+CO.fwdarw.1/2N.sub.2 +CO.sub.2
Platinum is the preferred catalyst for oxidation of CO and unburned hydrocarbons.
The noble metals are expensive and in limited supply, particularly rhodium. This is exacerbated by the fact than current usage of Pt and Rh in three-way catalysis exceeds the Rh/Pt mine ratio. Thus, reduction of noble metal usage is a problem of three-way catalysis. Therefore, it is necessary to develop alternative approaches to emission control.
U.S. Pat. Nos. 4,295,816, 4,382,017 and 4,475,483 describe catalyst solutions and delivery systems for improving the efficiency of combustion chambers. The catalyst solutions described in these patents comprise (a) a single metal catalyst compound, H.sub.2 PtCl.sub.6.6H.sub.2 O; a chloride compound such as HCl. LiCl, or NaCl; an antifreeze compound such as ethylene glycol; and approximately 50 percent water by volume, (b) a single platinum group metal catalyst in water and a layer of oil containing a manganese catalyst provided on top of the surface of the water, or (c) a single rhenium metal catalyst in water, or in a glycol solvent containing a chloride blocking agent, and a layer of oil containing a manganese catalyst provided on top of the surface of the water. The solutions are not taught or suggested for use in aiding conversion of automotive emissions, require a chloride "blocking agent" where a glycol solvent is employed, and contain undesirably high levels of water. Moreover, the solutions create an undesirable acidic and corrosive environment. The patents do not teach or suggest use of a solvent such as a diethylene glycol derivative, or that the solution could be used for deposition onto a surface within the exhaust system of an automobile.
Accordingly, there is a need for alternative methods of converting automotive emissions not utilizing conventional pre-fabricated, additional, non-regenerable solid catalytic material-containing supports in the exhaust system of an automobile.